Fundamental knowledge regarding events leading to effective immune response and memory development in poultry is lacking. This is particularly true for cellular responses and tissue responses in general. To study and monitor immune responses in an individual, non-terminal, minimally invasive procedures are essential. Peripheral blood and tissue secretions have served as an excellent window for humoral immune activities. Peripheral blood leukocytes can be used for various down-stream analyses. Blood plasma can be analyzed for antibodies and various soluble factors related to innate and adaptive immune response activities. However, because blood serves as a vehicle for leukocytes to travel to tissues containing the target antigen, this approach is limited, particularly regarding cellular/tissue activities. Thus, activated leukocytes or antigen-specific clones of lymphocytes represent only a minor portion of circulating cells. Hence to gain insight into innate and adaptive cellular immune activities and host/pathogen/immune interactions, in situ immune response activities will need to be examined.